1. Field of the Technology
The present technology relates to a developing unit used in an image forming apparatus such as a copier, printer, facsimile machine or the like using electrophotography as well as relating to an image forming apparatus including this developing unit. The technology in particular relates to a developing unit including a cooling mechanism of the developing vessel and a suctioning mechanism of scattering toner around the developing area using ducts.
2. Description of the Prior Art
With recent development of copiers, facsimile machines, printers and multi-functional machines having these functions into high-speed and high-resolution configurations, down-sizing of the carrier and toner used as the elemental technology for the electrophotographic process has been in progress. However, as the carrier and toner become smaller in size, in the developing area inside the image forming apparatus the carrier particles are prone to transfer to the image latent bearer, i.e., a photoreceptor drum during development, also toner is prone to scatter, causing image degradation and defects. Further, increase in processing speed brings about temperature increase in the developing unit, changes the developer characteristics and degrades the image quality, hence gives rise to the problem that the developer becomes solidified inside the developing unit and completely locks the developing unit itself, especially when the machine is used under a high temperature and high humidity environment.
In order to solve the above deficiencies, patent document 1 (Japanese Patent Application Laid-open Hei No. 10-274883) discloses a developing unit including: a developing vessel for holding a developer; a magnet roller disposed inside this developing vessel for supplying the developer to a photoreceptor drum; and a sanctioning fan with its suctioning ports arranged at both ends of the magnet roller so as to suction the developer scattering from the magnet roller through the suctioning ports. This developing unit enables efficient suctioning of scattering developer using a compact suctioning device and also enables reduction of the photoreceptor drum in diameter.
Another patent document 2 (Japanese Patent Application Laid-open 2006-23413) discloses an image forming apparatus which includes a developing unit having an integrally layered structure of a cooling duct and a scattering toner suctioning duct. That is, in this image forming apparatus, a cooling duct is provided in a space defined by the developing unit and a paper feed path for feeding recording paper to a transfer unit so as to cool the developing unit by sending cooling air into the duct while the cooling duct is formed with an opening that opposes the paper feed path so as to blow the cooling air to the recording paper that passes through the paper feed path. Further, a scattering toner suctioning duct for suctioning the toner scattering is formed under the cooling duct. With this image forming apparatus, it is possible to inhibit increase in the temperature inside the apparatus due to its heat-fixing process without hindering downsizing of the apparatus and reduction in the number of parts.
There is also another disclosure of an image forming apparatus in patent document 3 (Japanese Patent Application Laid-open 2004-361869), which includes a developer conveyer that has the developer electrostatically attracted to the electrostatic latent image formed on an image bearer; a housing that has a space for accommodating the developer conveyer and the developer and is formed with an opening parallel with the image bearer; a suctioning duct for suctioning floating toner and paper particulates in this housing; and a cooling duct for cooling the developing unit, wherein air is suctioned from the suctioning duct and cooling duct by a common suctioning means. In this image forming apparatus, it is possible to prevent increase in temperature while reducing toner scattering in the developing unit.
In the developing unit disclosed in patent document 1, a suctioning path for drawing scattering toner from below, and at both ends of, magnet (developing) roller and exhausting air through a filter located at the center is provided. However, there is no reference to a carrier collecting member. Further the suctioning means cannot suction the carrier and toner separately, so it is impossible to avoid carrier loss and filter clogging. Also, there is no mention of inclusion of any cooling means, so it is not clear whether cooling effect can be obtained or not.
In the image forming apparatus of patent document 2, the suctioning means and the cooling means are structured in two layers. However, there is no reference to a carrier collecting means, so it is impossible for the suctioning means to suction the carrier and toner separately from each other. Accordingly, reduction of the carrier in the developer and suctioning of toner together with the carrier cause the filter to be clogged up with the carrier. Further, since the cooling means is constructed to send air to the paper feed path but is not laid out to cool the entire bottom of the developing unit, it cannot be said that the cooling effect is sufficient.
Moreover, in the image forming apparatus of patent document 3, since the suctioning means and the cooling means are laid out in layers, but the cooling means is not constructed so as to cool the entire bottom of the developing unit, the cooling of the developing vessel is not effective enough. Also, there is no reference to a carrier collecting means, so it is impossible to suction the carrier and toner separately from each other. That is, this configuration has not reached to such a level as to solve the problems of carrier reduction, filter clogging and the like.
In sum, the developing units and image forming apparatuses disclosed in the above patent documents have yet to reach to such a level as to be able to prevent toner scattering as well as to realize effective enough cooling of the developing vessel and inhibit increase of the developing vessel in temperature. Also, since carrier and toner cannot be suctioned separately, any of the above configurations has not reached to so far as to solve the problems of carrier reduction and filter clogging.